A “Ssing sing barqeui” has been disclosed in Korean Patent Application Publication No. 10-2009-0086194. The related art is characterized in that, in order to solve the problem that a rider cannot maintain a stable posture on a bicycle in which gravity applied to a saddle disposed outside an outer wheel is transmitted to a point of the center of a wheel, gravity applied to the saddle is transmitted to two or more points including the center of a wheel, a rider is allowed to balance in the front-rear direction by positioning the rider to a front portion similar to bicycles to maintain an angle allowing the rider to conveniently press pedals for riding, a brake similar to common bicycles is installed by installing a device transmitting a driving force, and a shifting and coupling device inside a hub disposed inside a wheel, and a stable operation can be provided by controlling inertia.
However, the technology described above provides a structure essential to exhibit the principle of the invention, but shifting is complicated and it is difficult to make in a product.